Electron analysis apparatus with heat-protective shield means spacedly overlying a sample supporting surface

ABSTRACT

To enable visual observation and X-ray analysis of a sample irradiated by an electron beam, a heat-protective assembly overlying a sample-supporting surface includes an enclosure with a central window for the electron beam, a surrounding annular window for light rays and a pair of lateral windows for X-rays emanating from the sample. An inner shield has a frustoconical body, with generatrices converging toward the supporting surface, which gives passage to both the light rays and the electron beam while screening an area surrounding the annular lighttransmissive window of the enclosure without, however, blocking the passage of the X-rays. A set of deflecting plates for the electron beam is mounted on the inner shield, between its frustoconical body and a diaphragm forming the central window, in a zone between the paths of the light rays and the electron beam.

Daigne et al.

[ ELECTRON ANALYSIS APPARATUS WITH HEAT-PROTECTIVE SHIELD MEANS SPACEDLY OVERLYING A SAMPLE SUPPORTING SURFACE [75] Inventors: Bernard M. Daigne, Chatillon;

Francois M. Girard, Paris, both of France [73] Assignee: Office National DEtudes Et De Recherches Aerospatiales, Chatillon, France [22] Filed: Dec. 10, 1971 [21] Appl. No.: 206,601

[30] Foreign Application Priority Data Dec. 11, 1970 France 70.44739 [52] US. Cl. 250/310, 250/399 [51] Int. Cl. G01n 23/22 [58] Field of Search... 250/49.5 A, 49.5 B, 49.5 PE,

[56] References Cited UNITED STATES PATENTS 3,346,736 10/1967 Neuhausm. 250/49.5

3,629,579 12/1971 Naitou l 250/49.5

3,624,390 11/1971 Watanabe 250/49.5

[ 1 Mar. 26, 1974 Primary Examiner-William F. Lindquist Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [5 7] ABSTRACT To enable visual observation and X-ray analysis of a sample irradiated by an electron beam, a heatprotective assembly overlying a sample-supporting surface includes an enclosure with a central window for the electron beam, a surrounding annular window for light rays and a pair oflateral windows for X-rays emanating from the sample. An inner shield has a frustoconical body, with generatrices converging toward the supporting surface, which gives passage to both the light rays and the electron beam while screening an area surrounding the annular light-transmissive window of the enclosure without, however, blocking the passage of the X-rays. A set of deflecting plates for the electron beam is mounted on the inner shield, between its frustoconical body and a diaphragm forming the central window, in a zone between the paths of the light rays and the electron beam.

7 Claims, 5 Drawing Figures Pmmrwmzs m4 a a 00. 1 52 SHEET 2 BF 3 Bernard M. DAIGNE, Frangois M. GIRARD Inventors 0 ATTORNEY.

PAIENIEDHARZB m4 (1800.152

SHEET 3 OF 3 INVENTORS Bernard M. DAIGNE Frangzois M. GIRARD ELECTRON ANALYSIS APPARATUS WITH HEAT-PROTECTIVE SHIELD MEANS SPACEDLY OVERLYING A SAMPLE SUPPORTING SURFACE Our present invention relates to a system for protecting equipment for the study of samples irradiated by an electron beam.

Devices are known which provide information on the composition of a sample, based on the effects obtained by bombarding a restricted zone of the sample with a pencil-beam of electrons.

The information may be obtained by spectrographic analysis of the X-rays emitted by the bombarded zone, or, in the case ofa conductive sample, from the current set up in it as a result of the electron beam.

In some versions of such equipment, means exist for deflecting the electron beam so that it will bombard different impact zones on the sample.

These devices are housed in a vacuum chamber and include elaborate instruments designed to operate at the usual laboratory temperatures.

One of the aims of the present invention is to provide a protective system for such apparatus allowing sam ples to be studied or analyzed at high temperatures, as is desirable, for instance, in the case of metal compounds heated to temperature near their melting point.

The fairly small dimensionsof these devices, resulting mainlyfrom the conditions required for creating and maintaining the vacuum, and the passage of the electron beam raise certain problems, principally because of the proximity of the sample, which is at a high temperature, to components of the apparatus not designed to withstand intense heat.

The difficulty is further increased in apparatus of this kind provided with means for optical observation, as is often needed to locate the area of the sample to be analyzed.

An additional problem arises when metal compounds are being studied, since metal vapors may be given off which could damage sensitive parts of the apparatus, such as expensive optical appliances.

To overcome these difficulties we provide, in accordance with the invention, a protective assembly consisting of juxtaposed outer and inner shield means forming an enclosure for a sample-supporting surface designed to afford protection against the heat radiating from the sample and its base while also promoting the condensation of metal vapors to form deposits near the sample, thus preventing them from obscuring parts of the enclosure which must remain transparent while leaving a passage free for the electron beam, for lightray beams used in observation, and for X-ray beams for spectrographic analysis, if necessary.

According to one embodiment of the invention, the enclosure includes a diaphragm opposite the sample base, to protect the most fragile parts of the apparatus against heat radiation, with a hole in itforming a central window just large enough for the electron beam to pass through in a direction substantially perpendicular to the sample-supporting surface. The light rays traverse a light-transmissive window in the enclosure which is laterally offset from the central window and advantageously forms a ring therearound. At least one X-ray-transparent further window, laterally offset from the light-transmissive window, may be provided in the enclosure at a location accessible to radiation passing from the supporting surface around the outer periphery of the inner shield means which may be a frustoconical body surrounding the path of the light rays from the annular window.

In the case of an apparatus in which the electron beam can be deflected, an additional feature of the invention consists in providing electrostatic beamdeflecting means between the enclosure and the inner shield means, in a zone between the paths of the light rays and of the electron beam, so that the hole in the diaphragm can remain as small in size as for an apparatus in which the zone of impact of the electron beam is fixed.

We shall now describe one embodiment of the present invention, given by way of example, with reference to the accompanying drawing in which:

FIG. 1 is a diagrammatical view of a protective system according to the invention;

FIG. 2 is a cross-sectional diagrammatical view of part of an apparatus for analyzing samples by means of an electron beam, fitted with a protective system according to one embodiment of the invention;

FIG. 3 is a larger-scale view of part of FIG. 2;

FIG. 4 is a diagrammatical view, on a still larger scale, of the part of the protective system near the diaphragm and deflection plates; and

FIG. 5 is a cross-sectional view taken on the line 55 on FIG. 4.

In FIG. 1, the sample 10 to be studied is housed in a receptacle 1 1. A surrounding vacuum chamber, enclosing both the sample and the protective system, is not shown. A heating system in a base 12, beneath the receptacle 11, can heat the sample 10 to the required temperature. The sample may be a metal compound, for example, and the temperature resulting from the heating system in base 12 is high enough to reduce the composition, at least partly, to a liquid state.

The receptacle 11 is surmounted by a casing 13 whose wall 14 is designed to protect the apparatus against the heat produced by the heating system 12, and in particular against the heat radiating from the uncovered surface S of the sample which is at a high tem perature.

Above the receptacle 11, the casing 13 has a diaphragm 16 of a refractory material with an opening 17 whose cross-sectional area is roughly the same as that of the electron beam 18 aimed at the sample, at the point where it intersects the upper surface 19 of the diaphragm.

Inside the casing are located deflection means 21, preferably electrostatic plates as more fully described below, which can shift the zone of impact 22 of the electron beam over the surface S of the sample.

An inner shield in the form of a screen 23 is provided immediately next to the receptacle ll, protecting from heat radiation the parts of the outer shield or enclosure 13 which are not to be traversed either by light rays or by X-rays emitted by the sample, the apparatus containing means for optical observation of the surface S of the sample.

This screen 23 has the shape of a truncated cone whose generatrices 24, converging toward the samplesupporting surface of base 12, end in a circular edge 25 of small diameter; between this edge and the surface of the sample, sufficient space is left for the passage of X-ray beams 27 and 28 which traverse the casing 13 through lateral windows 31 and 32 transparent to X- rays.

The frustoconical screen periphery defined by generatrices 24 is so disposed in relation to the diaphragm 16 as to leave an annular field, bounded by conical surfaces 29 and 30, for the passage of light rays as needed for observation of the sample by microscope; these rays traverse the casing through an annular window 33 which is transparent to visible light.

The presence of the screen 23, close to the surface S of the sample, also helps protect the transparent casing parts 31, 32 and 33 against being obscured by deposits, in cases where the sample consists of metal compounds in a liquid state.

In some instances, the electron-beam-deflection device 21 could be omitted.

In FIG. 2, the receptacle 71 designed to hold the sample forms the upper part of a base 72 containing a heating system, with temperature-checking and control devices not shown. This base forms part of a samplesupporting unit 73; means diagrammatically indicated by arrows 74 and 75 are provided to move this unit in two directions longitudinally and transversely of a cross-bar 76 which forms part of the frame of the equipment. Another arrow 77 symbolizes means for adjusting the height of the unit.

The top and sides of the base 72 are surrounded by a protective shield structure 78. The distance between the side surface 79 of the shield and the receptacle 71 is much greater than that between the lower surface 80 of the shield and the receptacle.

The part of structure 78 farthest from the receptacle 71 (FIG. 3) consists of a metal frame 81, made of copper or some other good conductor, with internal passages 82 through which a cooling fluid circulates.

The upper part of the protective structure 78, overlying the receptacle 71, is preferably made from a highly heat-resistant material such as tantalum and carries a diaphragm 84. FIG. 4 shows the hole 85 of this diaphragm, traversed by an electron beam 86. The diaphragm is generally circular in shape, with a flat upper surface 61, at right angles to the axis 54 of the electron beam, and a frustoconical lower surface 62, connected by a plane underside 63 to its cylindrical periphery 64.

Beneath the diaphragm 84 we provide a deflector 87 which, in the embodiment described here, consists of two pairs of plates 41, 42 and 43, 44, shown in FIG. 5, supported on the free ends of four arms 45, 46 and 47, 48 on a surrounding frame 111. These plates have flat inner surfaces 65, parallel to the axis 54 of the beam, and outer surfaces 66 which diverge in a direction away from the receptacle 71; thus, their inner surfaces 65 define four walls of a square channel for the electron beam as best seen in FIG. 5. Shoulders 49 and 50 of arms 45 to 48 carry a stack of elements including, from the bottom up, a first annular insulating strip 56; a first metal grid 51; a ring-shaped plate 103, of a lighttransmissive material such as mica, with the diaphragm 84 set in it; a second metal grid 55; and finally a second annular insulating strip 57.

These stacked elements are held in place around the perimeter of the assembly. The grids 51 and 55, which remove the electric charges and heat collected by the transparent plate 103, have gaps 58 and 59 opposite the hole 85 in the diaphragm 84.

The refractory upper part of the shield structure 78 provides passages 91 and 92 for the X-ray beams emitted by the sample when bombarded with electrons, and an annular passage 96, encircling the diaphragm 84, for the light beams required for microscopic observation, the latter passage being bounded by conical surfaces 97 and 98.

A cover 99, resting on the upper side of the shield structure 78, contains windows 101 and 102 of a material transparent to X-rays, such as Mylar, and a ringshaped window 103, in line with the ray paths 91, 92 and 96, respectively. The windows 101 and 102 pro vide paths for the illumination of spectrographs 131 and 132.

The frame 111 (FIG. 3) has a cylindrical inner periphery 112 supporting, by means of a ring 113 with a flange 114, a frustoconical body 115, made of tantalum, with a base flange 116 and a vertex opening 117 immediately above the surface of the sample. The diameter of this opening determines the limiting positions of the electron beam during scanning. This scan is controlled by the two pairs of perpendicular deflection plates 41 44 carried by arms 45 48 on the inner shield 111, 113, 116, 117 of the protective assembly or shield structure 78.

This assembly is surmounted by two polar components 121 and 122 which are usual in a microprobe apparatus and which form part of a magnetic lens 123 (FIG. 2).

The shield structure 78 can be incorporated in an existing apparatus for enabling not only the performance of ordinary analyses but also the study of samples at high temperatures, without hindering the functioning of an associated microscope containing a lens 124 and mirrors 125 and 126.

The protective assembly according to this invention, providing protection against heat radiation and also, if necessary, against metallic deposits, may also be used in a scanning electron microscope.

Our improved system readily allows an existing apparatus to be adapted to new fields of application, thus considerably extending its usefulness.

We claim:

1. In an apparatus for the study of a sample under electron bombardment, in which a base forming a supporting surface for a sample to be studied is provided with heat-protective shield means including an outer enclosure spacedly overlying said supporting surface and an inner structure within said enclosure, said enclosure and said structure each having a central aperture for the passage of an electron beam and a lighttransmissive annular window surrounding said aperture, said enclosure having at least one X-raytransparent lateral window accessible to radiation emitted by a sample on said supporting surface, the improvement wherein said inner structure comprises:

a frame surrounding the path of light rays traversing said window, said frame being provided with inwardly extending radial arms; and

electrostatic beam-deflecting means supported on free ends of said arms and defining a central channel in line with said aperture for the passage of said electron beam, said beam-deflecting means being separated from said frame by an annular clearance in line with said annular window.

2. The improvement defined in claim 1 wherein said beam-deflecting means comprises two pairs of parallel on a vertex at said supporting surface.

5. The improvement defined in claim 4 wherein said frusto-conical body consists of refractory material.

6. The improvement defined in claim 5 wherein said refractory material is tantalum.

7. The improvement defined in claim 1 wherein said lateral window is duplicated on opposite sides of said annular window. 

1. In an apparatus for the study of a sample under electron bombardment, in which a base forming a supporting surface for a sample to be studied is provided with heat-protective shield means including an outer enclosure spacedly overlying said supporting surface and an inner structure within said enclosure, said enclosure and said structure each having a central aperture for the passage of an electron beam and a light-transmissive annular window surrounding said aperture, said enclosure having at least one X-ray- transparent lateral window accessible to radiation emitted by a sample on said supporting surface, the improvement wherein said inner structure comprises: a frame surrounding the path of light rays traversing said window, said frame being provided with inwardly extending radial arms; and electrostatic beam-deflecting means supported on free ends of said arms and defining a central channel in line with said aperture for the passage of said electron beam, said beamdeflecting means being separated from said frame by an annular clearance in line with said annular window.
 2. The improvement defined in claim 1 wherein said beam-deflecting means comprises two pairs of parallel plates in mutually orthogonal planes forming a set of four walls for said channel.
 3. The improvement defined in claim 2, further comprising a diaphragm separating said annular window from said aperture in said enclosure, said diaphragm being supported on said frame substantially in line with said plates.
 4. The improvement defined in claim 1 wherein said frame forms part of a frustoconical annular body with inner and outer generatrices substantially converging on a vertex at said supporting surface.
 5. The improvement defined in claim 4 wherein said frusto-conical body consists of refractory material.
 6. The improvement defined in claim 5 wherein said refractory material is tantalum.
 7. The improvement defined in claim 1 wherein said lateral window is duplicated on opposite sides of said annular window. 